Self-floating ocean bottom seismograph (OBS)

A self-floating ocean bottom seismograph (OBS) is installed on the seabed to observe natural earthquakes and explore sea-bottom structures. In addition to MCS reflection surveys, some 110 OBSs have been deployed to conduct refraction surveys in the seismogenic zones in the seas around Japan. JAMSTEC has used the resulting data to achieve a variety of research objectives.
Nippon Marine Enterprises has also been commissioned to maintain OBSs, as well as to provide OBS assembly, disassembly, observation, and data processing services. Nippon Marine Enterprises has provided input for OBS enhancements and a new model design.
OBS-based surveys can be classified into the two major categories below, although Nippon Marine Enterprises usually performs only the second type.

1.

Recording natural earthquakes

2.

Performing seismic refraction surveys in which strong sounds are generated with air guns and the waves returned from the geologic strata surface are recorded

A seismic refraction survey involves deployment, recording, and data recovery for about 110 OBSs during a roughly 25-day cruise. Cruise areas include the Nankai Trough, thought to be related to the Great Hanshin Awaji Earthquake (generally known as the Kobe Earthquake), the Japan Trench, and the sea off southeastern Hokkaido. The data obtained is used mainly for the research of sub-bottom structures and, in particular, for understanding the mechanism of huge earthquakes by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Click here to find out how an OBS works.

Waters where OBSs deployed

Points where OBSs were deployed to explore structure from 1999 to 2002 (KR02-05).